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Galvanic corrosion

Galvanic corrosion occurs when a corrosive electrolyte and two metallic materials are in contact. This corrosion increases on the least noble material (the anode) and decreases on the noblest (the cathode).

Generally, metallic corrosion involves the loss of metal at a spot on an exposed surface. Corrosion occurs in various forms ranging from uniform attacks over the entire surface to severe local attacks.

When a corrosive electrolyte and two metallic materials are in contact (galvanic cell), corrosion increases on the least noble material (the anode) and decreases on the noblest (the cathode). This increase in corrosion is called galvanic corrosion. The tendency of a metal or an alloy to corrode in a galvanic cell is determined by its position in the galvanic series. The galvanic series indicates the relative nobility of different metals and alloys in a given environment (e.g. seawater).The farther apart the metals are in the galvanic series, the greater the galvanic corrosion effect will be. Metals or alloys at the upper end are noble, while those at the lower end are least noble.

The principles of galvanic corrosion are used in cathodic protection. Cathodic protection is a means of reducing or preventing the corrosion of a metal surface by the use of sacrificial anodes (zinc or aluminium) or impressed currents.